This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to extend our previous studies on copper sites in biology, using a combination of S K-, Cu L-, and Cu K-edge and EXAFS spectroscopies, to define the electronic and geometric structure of Cu-containing proteins involved in electron transfer, O2 activation, N2O reduction and cofactor biogenesis. We plan to study H-bonding mutants of blue-copper proteins to evaluate the changes in electronic structure and its effect on the ET properties of BC proteins. A Cu K-edge EXAFS study will be performed on the reduced form of CuA at different pH?s to investigate the effect of pH on the ET and proton-pumping properties of the site. We also plan to study model complexes of mononuclear, binuclear, and multinuclear Cu and Heme-Cu containing proteins that are involved in O2 binding, transport and activation to understand mechanistic pathways of O2 interaction and activation. The model study will be extended and correlated to relevant protein systems to shed light on structure/function correlation of O2 binding and activation by the unique protein active sites.